Overview of Transport, Fast Particle and Heating and Current Drive Physics using Tritium in JET plasmas
Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority tritium (T) plasmas (nT/nD<3%). Thermal tritium particle transport coefficients (DT, vT) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities, and in the region of Internal Transport Barriers (ITB) in Reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q value (q95 ~ 2.8) and triangularity (δ = 0.2), T particle transport scales in a Gyro-Bohm manner in the inner plasma (r/a<0.4), whilst the outer plasma particle transport behaves more like Bohm scaling. Dimensionless parameter scans show contrasting behaviour for trace particle confinement (increases with collisionality ν* and β) and bulk energy confinement (decreases with ν* and independent of β). In an extended ELMy H-mode dataset, with ρ*,ν*, β and q varied, but with NTMs either absent or limited to weak, benign core modes (4/3 or above) the multiparameter fit to the normalised diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives DT/Bφ ~ ρ*- 2.46 . ν*- 0.23 .β - 1.01 . q 2.03 . In hybrid scenarios (qmin~1, low positive shear, no sawteeth), T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma, and Hybrid scenarios) in the outer plasma region, a correlation of high values of DT with high values of vT is seen. The normalised diffusion coefficients for the Hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalised tritium diffusion scales with normalised poloidal Larmor radius (ρθ*=qρ*) in a manner close to Gyro-Bohm (~ρθ* 3), with an added inverse β dependence. The effects of ELMs, sawteeth and Neo-classical Tearing Modes (NTMs) on T particle transport are described. Fast-ion confinement in Current-Hole (CH) plasmas, was tested in TTE by injection of Tritium NBI into JET CH plasmas. γ-rays from the reactions of fusion alphas and beryllium impurities (9Be(α,nγ)12C) characterised the fast fusion-alpha population evolution. The γ-decay times are consistent with classical alpha plus parent fast triton slowing down times (τTs+ταs) for high plasma currents (Ip >2MA) and monotonic q-profiles. In CH discharges the γ-ray emission decay times are much lower than classical (τTs+ταs), indicating alpha confinement degradation, due to orbit losses predicted by a 3-D Fokker Planck numerical code, and modelled by TRANSP.